This invention relates generally to optically variable pigments, films, inks, paints, devices, and images, and more particularly to images with aligned or oriented pigment flakes, for example, during a painting or printing process, to obtain an illusive optical effect. This invention is particularly applicable to aligning magnetically alignable pigment flakes and is also applicable to aligning non-magnetic dielectric or semiconductor flakes in an electric field.
Optically variable devices are used in a wide variety of applications, both decorative and utilitarian. Optically variable devices can be made in variety of ways to achieve a variety of effects. Examples of optically variable devices include the holograms imprinted on credit cards and authentic software documentation, color-shifting images printed on banknotes, and enhancing the surface appearance of items such as motorcycle helmets and wheel covers.
Optically variable devices can be made as film or foil that is pressed, stamped, glued, or otherwise attached to an object, and can also be made using optically variable pigments. One type of optically variable pigment is commonly called a color-shifting pigment because the apparent color of images appropriately printed with such pigments changes as the angle of view and/or illumination is tilted. A common example is the “20” printed with color-shifting pigment in the lower right-hand corner of a U.S. twenty-dollar bill, which serves as an anti-counterfeiting device.
Some anti-counterfeiting devices are covert, while others are intended to be noticed. This invention relates to overt features, intended to be noticed, however flakes having covert features therein, such as indicia can be used. Furthermore flakes with gratings and holographic features can be used. Unfortunately, some optically variable devices that are intended to be noticed are not widely known because the optically variable aspect of the device is not sufficiently dramatic. For example, the color shift of an image printed with color-shifting pigment might not be noticed under uniform fluorescent ceiling lights, but more noticeable in direct sunlight or under single-point illumination. This can make it easier for a counterfeiter to pass counterfeit notes without the optically variable feature because the recipient might not be aware of the optically variable feature, or because the counterfeit note might look substantially similar to the authentic note under certain conditions.
Optically variable devices can also be made with magnetic pigments that are aligned with a magnetic field after applying the pigment (typically in a carrier such as an ink vehicle or a paint vehicle) to a surface. However, painting with magnetic pigments has been used mostly for decorative purposes. For example, use of magnetic pigments has been described to produce painted cover wheels having a decorative feature that appears as a three-dimensional shape. A pattern was formed on the painted product by applying a magnetic field to the product while the paint medium still was in a liquid state. The paint medium had dispersed magnetic non-spherical particles that aligned along the magnetic field lines. The field had two regions. The first region contained lines of a magnetic force that were oriented parallel to the surface and arranged in a shape of a desired pattern. The second region contained lines that were non-parallel to the surface of the painted product and arranged around the pattern. To form the pattern, permanent magnets or electromagnets with the shape corresponding to the shape of desired pattern were located underneath the painted product to orient in the magnetic field non-spherical magnetic particles dispersed in the paint while the paint was still wet. When the paint dried, the pattern was visible on the surface of the painted product as the light rays incident on the paint layer were influenced differently by the oriented magnetic particles.
Similarly, a process for producing of a pattern of flaked magnetic particles in fluoropolymer matrix has been described. After coating a product with a composition in liquid form, a magnet with desirable shape was placed on the underside of the substrate. Magnetic flakes dispersed in a liquid organic medium orient themselves parallel to the magnetic field lines, tilting from the original planar orientation. This tilt varied from perpendicular to the surface of a substrate to the original orientation, which included flakes essentially parallel to the surface of the product. The planar oriented flakes reflected incident light back to the viewer, while the reoriented flakes did not, providing the appearance of a three dimensional pattern in the coating.
It is desirable to create more noticeable optically variable security features on financial documents and other products and to provide features that are difficult for counterfeiters to copy.
It is also desirable to create features which add to the realism of printed images made with inks and paints having alignable flakes therein, especially printed images of objects and more particularly recognizable three dimensional objects.
Heretofore, in patent application PCT/US2003/020665 the inventor of the present application has described embodiments of an invention known as the “rolling-bar” and the “flip-flop” which provide kinematical features, that is features which provide the optical illusion of movement, to images comprised of magnetically alignable pigment flakes wherein the flakes are aligned in a particular manner. Although this is heralded as a significant advance in the field of alignment of pigment flakes, and more generally related to anti-counterfeiting coatings, the inventors have discovered new and exciting applications of the rolling-bar and other rolling objects such as a rolling hemisphere which yields realistic 3-D like images formed of alignable pigment flakes, not realized before. The rolling hemisphere appears to move all directions on an x-y plane in dependence upon an angle at which the image is tilted or the angle at which the light source upon the image varied.
Although the rolling bar described in the aforementioned PCT patent application provides the illusion of a moving bar across a rectangular image, this invention has limitations. It is a single kinematic feature which can be observed. It is also somewhat difficult to copy. But essentially it provides the observer with the experience of seeing a rolling bar of uniform size and intensity which is unvarying as it appears to move along the substrate upon the rectangular image it is apart of.
In this invention, the inventors have since discovered that providing a rolling bar used as a fill within an outline of a curved recognizable object, particularly a smooth curved recognizable object such as a bell, a shield, container, or a soccer ball provides striking effects that reach beyond a rolling bar moving back and forth on a rectangular sheet. The bar while providing realistic dynamic shading to an image of an object not only appears to move across the image but also appears to grow and shrink or expand and contract with this movement within the closed region in which it is contained. In some instances where the size or area of the bar doesn't vary, for example wherein it is used a as a partial fill within an image between two conforming curved lines that move together with a space between, filled by the bar, the bar appears to move across the image while simultaneously moving up and down. Thus, this invention provides a highly desired optical effect by using the rolling bar inside a non rectangular outlined closed shape of an object, wherein the area of the rolling bar changes as the bar moves across the image, and, or wherein the bar appears to move horizontally and vertically simultaneously as the image is tilted or the light source upon the image is varied. Additionally, if the bar is designed to be of a suitable size and radius of curvature, it can be used as a dynamic, moving, shrinking or expanding shading element in the image, providing exceptional realism. It has also been found, that the rolling bar appears to have a most profound effect when it appears to mimic moving shading on an image of a real object that is capable or producing a shadow when light is incident upon it. In these important applications, it is preferred that the radius of curvature of the flakes forming the rolling bar be within a range of values wherein the image of the real-object it is applied to, appears to be correctly curved so as to appear realistic. It is an object of this invention, to provide an optically illusive image having kinematical features that depend upon tilting the image or varying the location of the light source upon the image.
The term rectangular used in this specification is defined to mean a quadrilateral with four right angles. Thus a non-rectangular object or image does not have 4 sides and four right angles.
This invention refers to forming images of objects wherein the images of the object include special effects such as rolling bar effects that provide the illusion of moving shadows as the image of object is tilted or the light source upon the image is varied. The definition of object in this context is a tangible and visible entity; an entity that can cast a shadow.
The term rolling bar shall not be limited to a straight bar as it may be a curved bar, depending upon the shape of the applied field.